New Kid on the Block

[MonzaMan]

Hi. I can't find any specific thread or place for new member introductions, so I would like to introduce myself to this amazing community as a new member as of today. I will then cut to the chase and make my first technical inquiry. I registered because I have a 1968 widecase Monza that I have owned for about 35 years. I live in Ontario, Canada.

The bike has been neglected in storage for the last 20 years and I am now resurrecting the bike. It was in perfect running order when I put it away, shortly after a major restoration. The first two pictures attached are from just after the resto.

The gas tank has been thoroughly cleaned inside and carb rebuild (square slide VHB30) is underway. During the resto way back then I replaced the wiring harness with one I built with 12 ga. wire. It is a stock 6V reg - I guess the 75W. The electrics were always reliable. It has the 4-terminal R/R.

I noticed the two yellow wires and the red from the stator had disintegrating insulation (crumble to the touch). The conductors looked awful too, as if they had been overloaded at one point. So I rewired the sub-harness from the stator with new wire and heat-shrink.

Here's my question(s)...

I want to wire up the charge control idiot lamp so that it works as per original. I am not hung up on correctness or authenticity but I want the charging circuit to be original. I acquired the correct 1.5W bulb and a new ignition switch (Aprilia 17121, see pictures). I have consulted all the wiring schematics for all years available and they all show the wiring of the charging light differently, and some versions don't seem to make any sense.

For starters, does anyone know how the light works? Does it turn on when the ignition is on and then go off when the bike starts and the battery is charging (like an alt light on a car)? Is it just an idiot light that stupidly stays on all the time to tell you the switch is on? Does it come on when the battery stops charging? This last function is what I want.

Can anyone suggest how to wire up this bulb? The festoon style bulb hangs off the side of the Aprilia and most diagrams show it fed 6V when the ignition switch is on.

Any help would be very much appreciated.

A huge thanks to all of you who have contributed on this site with so much precious information for us Ducati lovers who need it. You have created an incredible resource.

Please have a look at the images....


https://i.imgur.com/RCk6vTV.jpg

https://i.imgur.com/eldna8a.jpg

https://i.imgur.com/2HE8uZN.jpg

https://i.imgur.com/tlNAG8P.jpg

https://i.imgur.com/gwR1zk4.jpg

https://i.imgur.com/XPVFIZg.jpg

https://i.imgur.com/m4D5WEs.jpg




Best regards,

David (MonzaMan)

[Jordan]

Hi David, that's a rarish model you have. Seen sometimes in the USA, not in Australia.

I don't know of any Ducati single that had a working charge indicator as standard.

If you want one, maybe this person can supply: https://www.improvingclassicmotorcycles ... oducts.htm
He's very supportive, insisted on supplying a new charge indicator free when I just mentioned I had one of his fail on a British bike I own - after some years.

[MonzaMan]

Thanks Jordan.

In the technical section of this very site there are two widecase electrical schematics and narrowcase schematics as well. They all show a 'charge control' indicator light. It seems usually powered with 6V from the ignition switch. The 'Marrone' wire (brown) from the R/R typically goes to this light also, but via the coil. This brown wire while I am not certain, I believe is actually a sense wire; a low current input that helps the R/R charge the battery at a high enough voltage to overcome the voltage drop in the harness. It seems logical that this wire be connected to the coil because the other wire on the same coil terminal from the ignition switch has a very long route from the battery through the fuse block and ignition switch, then to the coil and so a large voltage drop. This would tend to make the R/R deliver more voltage to the batter - a good thing.

I am really interested to know how the light is supposed to work. An always on light is useless to me. But a charge indicator is useful and the diagrams tend to use this language to label it.

I wonder if the bulb should be fed from both sides, battery on one side and Marrone on the other. If there is no ground wire and the alternator dies then current would flow through the bulb and depending on the internal working of the R/R (just a mysterious black box to me) back to ground through the stator. If this were the case the light would go on when the alternator is dead or very weak. Just like a car. Turn on the ignition and the light goes on. Start the bike, and if the alternator is working the light goes out.

I am interested to know both how the circuit is supposed to be arranged, how it really works - but also how these things actually worked from the factory. If it were possible to read the owner's manual description of the light that would possibly shed light on matters, but then again there were so many models. This a 1968 widecase street bike with the 'square styling' for the US market.

Kind regards,

David

[blethermaskite]

Hi david, welcome, so the little red idiot light that comes on when your ignition is energized is frankly just an idiot light! it stays on all the time......just in case you hadn't noticed the bike was running or you had left the ignition on........its also quite annoying during night riding, of course it should go out to advise the charging system is working .....but it doesn't
Cheers,
George

[MonzaMan]

Okay! Thank you for the answer - disappointing but at least I know!

Best,

D

[MonzaMan]

Hello again!

I have found some new information - apparently, this WAS actually a functional charge light indicator. Starting a new thread...

Thanks everyone!

David